A bobbin for an electrical coil is known comprising a tubular core with terminating flanges or cheeks at each end of the tubular core to define a main winding space of the bobbin.
The tubular core and the two end cheeks may be made of a plastics material and the end cheeks provided with metal posts.
During winding of the bobbin, electrical wire is wound a few turns around one post and then led through an opening in an adjacent cheek to the main winding space. When the required number of turns on the tubular core have been wound to form the main winding, the wire is led through a passageway in the other cheek and wound a few turns on the other post.
The wound turns on the posts are then anchored in place by soldering and the wire is severed at each post, to form respective terminal connections for the wire on the main winding.
Winding of the bobbins heretofore has involved manual handling, notably hand winding around the posts and soldering thereat to form the terminal connections. Apart from being tedious and time consuming, breakage of the wire is prevalent in these procedures, especially when handling miniature bobbins and winding wire of hair-like proportions sometimes of the order of 1/1000th of an inch in diameter.
A further problem with the known bobbins is that the terminal connections, which can be formed on them, have a structural weakness and are unsuitable in certain applications since they tend to break easily under stress, for example, in the manufacture of miniature reed relays for use in printed circuit boards.
The basic components of a well-known miniature reed relay comprise a reed switch surrounded by an energising electromagnetic coil wound on a bobbin of the type mentioned above.
To form the relay the terminal connections to the reed switch and coil are first soldered in place by hand at selected positions in a lead frame having connector pins normally corresponding in number to the terminal connections.
The lead frame is then inserted between two halves of a transfer mould and encapsulating material such as epoxy resin, is introduced into the mould under pressure to form a housing around the reed relay and its connections to the connector pins.
It is during mould encapsulation that the weakness of the terminal connections becomes apparent. Specifically they are unable to withstand adequately the pressures involved and breakage of the wire leading from the main winding to the bobbin posts is prevalent, this wire being but a single strand.
The above-mentioned problems with the prior art bobbin lead to excessive wastage, both from the standpoint of time and materials. Automated procedures would assist in obviating the former disadvantage and also in part the latter, but the basic structure of the bobbin does not lend itself to such a solution. Moreover the structural weakness of the terminal connections would still remain.